Re: [PATCH v3 00/13] virtio-fs: shared file system for virtual machines
From: Miklos Szeredi
Date: Tue Sep 03 2019 - 04:05:18 EST
[Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx, "Michael S. Tsirkin"
<mst@xxxxxxxxxx>, Jason Wang <jasowang@xxxxxxxxxx>]
It'd be nice to have an ACK for this from the virtio maintainers.
On Wed, Aug 21, 2019 at 7:38 PM Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> Here are the V3 patches for virtio-fs filesystem. This time I have
> broken the patch series in two parts. This is first part which does
> not contain DAX support. Second patch series will contain the patches
> for DAX support.
> I have also dropped RFC tag from first patch series as we believe its
> in good enough shape that it should get a consideration for inclusion
> These patches apply on top of 5.3-rc5 kernel and are also available
> Patches for V1 and V2 were posted here.
> More information about the project can be found here.
> Changes from V2
> - Various bug fixes and performance improvements.
> We have put instructions on how to use it here.
> Some Performance Numbers
> I have basically run bunch of fio jobs to get a sense of speed of
> various operations. I wrote a simple wrapper script to run fio jobs
> 3 times and take their average and report it. These scripts are available
> I set up a directory on ramfs on host and exported that directory inside
> guest using virtio-9p and virtio-fs and ran tests inside guests. Ran
> tests with cache=none both for virtio-9p and virtio-fs so that no caching
> happens in guest. For virtio-fs, I ran an additional set of tests with
> dax enabled. Dax is not part of first patch series but I included
> results here because dax seems to get the maximum performance advantage
> and its shows the real potential of virtio-fs.
> Test Setup
> - A fedora 28 host with 32G RAM, 2 sockets (6 cores per socket, 2
> threads per core)
> - Using ramfs on host as backing store. 4 fio files of 2G each.
> - Created a VM with 16 VCPUS and 8GB memory. An 8GB cache window (for dax
> Test Results
> - Results in three configurations have been reported. 9p (cache=none),
> virtio-fs (cache=none) and virtio-fs (cache=none + dax).
> There are other caching modes as well but to me cache=none seemed most
> interesting for now because it does not cache anything in guest
> and provides strong coherence. Other modes which provide less strong
> coherence and hence are faster are yet to be benchmarked.
> - Three fio ioengines psync, libaio and mmap have been used.
> - I/O Workload of randread, radwrite, seqread and seqwrite have been run.
> - Each file size is 2G. Block size 4K. iodepth=16
> - "multi" means same operation was done with 4 jobs and each job is
> operating on a file of size 2G.
> - Some results are "0 (KiB/s)". That means that particular operation is
> not supported in that configuration.
> NAME I/O Operation BW(Read/Write)
> 9p-cache-none seqread-psync 27(MiB/s)
> virtiofs-cache-none seqread-psync 35(MiB/s)
> virtiofs-dax-cache-none seqread-psync 245(MiB/s)
> 9p-cache-none seqread-psync-multi 117(MiB/s)
> virtiofs-cache-none seqread-psync-multi 162(MiB/s)
> virtiofs-dax-cache-none seqread-psync-multi 894(MiB/s)
> 9p-cache-none seqread-mmap 24(MiB/s)
> virtiofs-cache-none seqread-mmap 0(KiB/s)
> virtiofs-dax-cache-none seqread-mmap 168(MiB/s)
> 9p-cache-none seqread-mmap-multi 115(MiB/s)
> virtiofs-cache-none seqread-mmap-multi 0(KiB/s)
> virtiofs-dax-cache-none seqread-mmap-multi 614(MiB/s)
> 9p-cache-none seqread-libaio 26(MiB/s)
> virtiofs-cache-none seqread-libaio 139(MiB/s)
> virtiofs-dax-cache-none seqread-libaio 160(MiB/s)
> 9p-cache-none seqread-libaio-multi 129(MiB/s)
> virtiofs-cache-none seqread-libaio-multi 142(MiB/s)
> virtiofs-dax-cache-none seqread-libaio-multi 577(MiB/s)
> 9p-cache-none randread-psync 29(MiB/s)
> virtiofs-cache-none randread-psync 34(MiB/s)
> virtiofs-dax-cache-none randread-psync 256(MiB/s)
> 9p-cache-none randread-psync-multi 139(MiB/s)
> virtiofs-cache-none randread-psync-multi 153(MiB/s)
> virtiofs-dax-cache-none randread-psync-multi 245(MiB/s)
> 9p-cache-none randread-mmap 22(MiB/s)
> virtiofs-cache-none randread-mmap 0(KiB/s)
> virtiofs-dax-cache-none randread-mmap 162(MiB/s)
> 9p-cache-none randread-mmap-multi 111(MiB/s)
> virtiofs-cache-none randread-mmap-multi 0(KiB/s)
> virtiofs-dax-cache-none randread-mmap-multi 215(MiB/s)
> 9p-cache-none randread-libaio 26(MiB/s)
> virtiofs-cache-none randread-libaio 135(MiB/s)
> virtiofs-dax-cache-none randread-libaio 157(MiB/s)
> 9p-cache-none randread-libaio-multi 133(MiB/s)
> virtiofs-cache-none randread-libaio-multi 245(MiB/s)
> virtiofs-dax-cache-none randread-libaio-multi 163(MiB/s)
> 9p-cache-none seqwrite-psync 28(MiB/s)
> virtiofs-cache-none seqwrite-psync 34(MiB/s)
> virtiofs-dax-cache-none seqwrite-psync 203(MiB/s)
> 9p-cache-none seqwrite-psync-multi 128(MiB/s)
> virtiofs-cache-none seqwrite-psync-multi 155(MiB/s)
> virtiofs-dax-cache-none seqwrite-psync-multi 717(MiB/s)
> 9p-cache-none seqwrite-mmap 0(KiB/s)
> virtiofs-cache-none seqwrite-mmap 0(KiB/s)
> virtiofs-dax-cache-none seqwrite-mmap 165(MiB/s)
> 9p-cache-none seqwrite-mmap-multi 0(KiB/s)
> virtiofs-cache-none seqwrite-mmap-multi 0(KiB/s)
> virtiofs-dax-cache-none seqwrite-mmap-multi 511(MiB/s)
> 9p-cache-none seqwrite-libaio 27(MiB/s)
> virtiofs-cache-none seqwrite-libaio 128(MiB/s)
> virtiofs-dax-cache-none seqwrite-libaio 141(MiB/s)
> 9p-cache-none seqwrite-libaio-multi 119(MiB/s)
> virtiofs-cache-none seqwrite-libaio-multi 242(MiB/s)
> virtiofs-dax-cache-none seqwrite-libaio-multi 505(MiB/s)
> 9p-cache-none randwrite-psync 27(MiB/s)
> virtiofs-cache-none randwrite-psync 34(MiB/s)
> virtiofs-dax-cache-none randwrite-psync 189(MiB/s)
> 9p-cache-none randwrite-psync-multi 137(MiB/s)
> virtiofs-cache-none randwrite-psync-multi 150(MiB/s)
> virtiofs-dax-cache-none randwrite-psync-multi 233(MiB/s)
> 9p-cache-none randwrite-mmap 0(KiB/s)
> virtiofs-cache-none randwrite-mmap 0(KiB/s)
> virtiofs-dax-cache-none randwrite-mmap 120(MiB/s)
> 9p-cache-none randwrite-mmap-multi 0(KiB/s)
> virtiofs-cache-none randwrite-mmap-multi 0(KiB/s)
> virtiofs-dax-cache-none randwrite-mmap-multi 200(MiB/s)
> 9p-cache-none randwrite-libaio 25(MiB/s)
> virtiofs-cache-none randwrite-libaio 124(MiB/s)
> virtiofs-dax-cache-none randwrite-libaio 131(MiB/s)
> 9p-cache-none randwrite-libaio-multi 125(MiB/s)
> virtiofs-cache-none randwrite-libaio-multi 241(MiB/s)
> virtiofs-dax-cache-none randwrite-libaio-multi 163(MiB/s)
> - In general virtio-fs seems faster than virtio-9p. Using dax makes it
> really interesting.
> Right now dax window is 8G and max fio file size is 8G as well (4
> files of 2G each). That means everything fits into dax window and no
> reclaim is needed. Dax window reclaim logic is slower and if file
> size is bigger than dax window size, performance slows down.
> Description from previous postings
> Design Overview
> With the goal of designing something with better performance and local file
> system semantics, a bunch of ideas were proposed.
> - Use fuse protocol (instead of 9p) for communication between guest
> and host. Guest kernel will be fuse client and a fuse server will
> run on host to serve the requests.
> - For data access inside guest, mmap portion of file in QEMU address
> space and guest accesses this memory using dax. That way guest page
> cache is bypassed and there is only one copy of data (on host). This
> will also enable mmap(MAP_SHARED) between guests.
> - For metadata coherency, there is a shared memory region which contains
> version number associated with metadata and any guest changing metadata
> updates version number and other guests refresh metadata on next
> access. This is yet to be implemented.
> How virtio-fs differs from existing approaches
> The unique idea behind virtio-fs is to take advantage of the co-location
> of the virtual machine and hypervisor to avoid communication (vmexits).
> DAX allows file contents to be accessed without communication with the
> hypervisor. The shared memory region for metadata avoids communication in
> the common case where metadata is unchanged.
> By replacing expensive communication with cheaper shared memory accesses,
> we expect to achieve better performance than approaches based on network
> file system protocols. In addition, this also makes it easier to achieve
> local file system semantics (coherency).
> These techniques are not applicable to network file system protocols since
> the communications channel is bypassed by taking advantage of shared memory
> on a local machine. This is why we decided to build virtio-fs rather than
> focus on 9P or NFS.
> Caching Modes
> Like virtio-9p, different caching modes are supported which determine the
> coherency level as well. The âcache=FOOâ and âwritebackâ options control the
> level of coherence between the guest and host filesystems.
> - cache=none
> metadata, data and pathname lookup are not cached in guest. They are always
> fetched from host and any changes are immediately pushed to host.
> - cache=always
> metadata, data and pathname lookup are cached in guest and never expire.
> - cache=auto
> metadata and pathname lookup cache expires after a configured amount of time
> (default is 1 second). Data is cached while the file is open (close to open
> - writeback/no_writeback
> These options control the writeback strategy. If writeback is disabled,
> then normal writes will immediately be synchronized with the host fs. If
> writeback is enabled, then writes may be cached in the guest until the file
> is closed or an fsync(2) performed. This option has no effect on mmap-ed
> writes or writes going through the DAX mechanism.
> Miklos Szeredi (2):
> fuse: delete dentry if timeout is zero
> fuse: Use default_file_splice_read for direct IO
> Stefan Hajnoczi (6):
> fuse: export fuse_end_request()
> fuse: export fuse_len_args()
> fuse: export fuse_get_unique()
> fuse: extract fuse_fill_super_common()
> fuse: add fuse_iqueue_ops callbacks
> virtio_fs: add skeleton virtio_fs.ko module
> Vivek Goyal (5):
> fuse: Export fuse_send_init_request()
> Export fuse_dequeue_forget() function
> fuse: Separate fuse device allocation and installation in fuse_conn
> virtio-fs: Do not provide abort interface in fusectl
> init/do_mounts.c: add virtio_fs root fs support
> fs/fuse/Kconfig | 11 +
> fs/fuse/Makefile | 1 +
> fs/fuse/control.c | 4 +-
> fs/fuse/cuse.c | 4 +-
> fs/fuse/dev.c | 89 ++-
> fs/fuse/dir.c | 26 +-
> fs/fuse/file.c | 15 +-
> fs/fuse/fuse_i.h | 120 +++-
> fs/fuse/inode.c | 203 +++---
> fs/fuse/virtio_fs.c | 1061 +++++++++++++++++++++++++++++++
> fs/splice.c | 3 +-
> include/linux/fs.h | 2 +
> include/uapi/linux/virtio_fs.h | 41 ++
> include/uapi/linux/virtio_ids.h | 1 +
> init/do_mounts.c | 10 +
> 15 files changed, 1462 insertions(+), 129 deletions(-)
> create mode 100644 fs/fuse/virtio_fs.c
> create mode 100644 include/uapi/linux/virtio_fs.h